This invention relates to connecting unions, and more particularly to chromatographic column fittings. It is particularly adapted, among many other possible uses, for coupling the inlet and the outlet of a glass capillary column to the remainder of the system. It is also particularly applicable to metal capillary systems.
In the art of gas chromatography, it is conventional for a sample together with carrier gas to be injected into a glass capillary column where it is heated, and the effluent therefrom directed to one of various types of detectors, for analyzing the characteristics of the particular sample. Such instruments are very sensitive and, hence, the performance accuracy is of the utmost importance. Heretofore, difficulties were experienced with such instruments due to the inaccuracies resulting from conventional fittings used for the connections to and from the glass capillary column. It will be appreciated that in many installations glass lined stainless steel tubing of relatively large diameter, such as about 1.59 mm. outside diameter for example, is coupled to a glass capillary column of relatively small diameter, such as about 0.75 mm. outside diameter for example. It should also be appreciated that the sample size in such installations is relatively small, thereby compounding the difficulties involved. Conventional fittings including so-called "zero dead volume" types caused degradation of the column performance, particularly with respect to loss of column efficiency and degradation of the peak shape, such as tailing, in the chromatogram.
Our invention involves a novel combination of features combined in such a way as to afford a very efficient and effective solution to the deficiencies encountered with the prior art, as will become apparent as the description proceeds.